I think as long as gitlab has a diff API and a file list API it would be pretty simple. Unfamiliar with their APIs though.
Get the diff of a commit - https://docs.gitlab.com/ee/api/commits.html#get-the-diff-of-...
List repository tree - https://docs.gitlab.com/ee/api/repositories.html#list-reposi...
Repository files API - https://docs.gitlab.com/ee/api/repository_files.html